The Linux kernel recently had a significant security issue or two wherethe root cause was that user programs could map memory at page zero, andthis lead to kernel level exploits. If you went through the same sort ofundergrad OS course that I did, you might be wondering how on earth auser process memory mapping issue leads to a kernel exploit; after all,as all of those little box diagrams tell us, the user program addressspace is one thing and the kernel address space is an entirely differentthing.

We've recently had another interesting case of 'accidental BitTorrent' on our network, different from the previoustimes. This time around it was through our VPN server, and just fromthat alone you can probably guess what happened.

Suppose that you are a user, sitting at home running BitTorrent in thebackground on your home machine while you do other things. You need toaccess some restricted on-campus thing; our generally supported way todo this is to fire up a VPN connection so that you are '

One of the test driven development mantras that I've heard is 'if youhaven't tested it, it doesn't work'. Which leaves me with a questionthat I don't know the answer to: how do you test an extendible format?

Suppose that you have a data file format (for example, an XML dialect)that allows more or less arbitrary extensions to be embedded in it, andalso that you have some agreement on how your program is supposed tohandle extension elements that